Hematopoietic stem cell proliferation, differentiation and apoptosis, are regulated by various growth factors and cytokines (Metcalf, D., Science 254, 529-531 (1992) and Vaux et al., Nature 335, 440-442 (1988)). Such cells committed to the myeloid lineage express high affinity receptors for GM-CSF1 and IL-3 (Miyajima et al., Blood 82,1960-1973 (1993)). Moreover, such cells develop a requirement for GM-CSF or IL-3 to survive and undergo apoptosis in response to GM-CSF or IL-3 deprivation (Williams et al., Nature 343, 76-79 (1990)).
Hematopoietic cells are not unique in their requirement for growth factors for survival. Throughout development, cells of all lineages require proper signals to grow and differentiate. Failure to receive these signals often results in death of the cells by apoptosis. Even in the adult organism there is constant renewal and/or maintence of cells that requires growth factors and cytokines. Inappropriate cessation of signals from these growth factors may result in apoptosis thereby causing disfunction or disease.
Several apoptotic genes appear to be conserved in multicellular organisms. For example, the ced-3 gene of Caenorhabditis elegans has a family of mammalian homologue cysteine protease, including interleukin-1.beta.-converting enzyme (ICE), Ich-1, CPP32, TX, ICErelIII, and LAP3 (Yuan, et al., Cell 75, 641-652 (1993) and Miura, et al., Cell 75, 653-660 (1993); Wang, et al., Cell 78, 739-750 (1994), Fernandes-Alnemri, et al., JBC 269, 30761-30764 (1994), Faucheu, et al., EMBO J 14, 1914-1922 (1995), Munday, et al., JBC270, 15870-15876 (1995) and Duan, et al., JBC 271, 35013-35035 (1996)). Antagonists of the apoptosis are also conserved, such as, for example, ced-9 of C. elegans and its mammalian homologue bcl-2. Molecular control of initiation is less well resolved.
Cell lines that proliferate in response to IL-3 and undergo rapid programmed cell death following IL-3 deprivation can be used for expression cloning systems. Using such a system, genes that antagonize apoptosis may be found. Murine cells have been shown to be useful for this purpose. A murine Requiem gene believed to encode a transcription factor required for apoptosis response following survival factor withdrawal from myeloid cells has been described (Gabig, et al., JBC 269, 29515-29519 (1994)).
The present invention provides a human homolog of the Requiem gene and polypeptides encoded therefrom (herein "REQUIEM"). The human sequence contains more 5' sequence than the mouse requiem sequence and has a more 5' start site which is believed to be the correct start site.